Most file types are accepted, including .doc, .docx, .pdf, .txt, .ppt, .gif, and .png. The acceptable file types are the same everywhere attachments are available (proposals, job posts, messages, etc.).
Unsupported file types
.ade, .adp, .bat, .chm, .cmd, .com, .cpl, .exe, .hta, .ins, .isp, .jar, .jse, .lib, .lnk, .mde, .msc, .msp, .mst, .pif, .scr, .sct, .shb, .sys, .vb, .vbe, .bs, .vxd, .wsc, .wsf, .wsh
Note: The .zip file type is not currently supported for iOS devices.